US Patent 7842577 Two-step STI formation process

A method of forming an integrated circuit structure includes providing a semiconductor substrate; forming a first isolation region in the semiconductor substrate; after the step of forming the first isolation region, forming a metal-oxide-semiconductor (MOS) device at a surface of the semiconductor substrate, wherein the step of forming the MOS device comprises forming a source/drain region; and after the step of forming the MOS device, forming a second isolation region in the semiconductor substrate.